Mutations at Asp112 adjacent to the trinuclear Cu center in CueO as the proton donor in the four-electron reduction of dioxygen.

Asp112 adjacent to the trinuclear Cu center of a multicopper oxidase, CueO was mutated for Glu, Ala and Asn. Mutations on Asp112 affected not only spectroscopic and magnetic properties derived from the trinuclear Cu center but also enzyme activities. The uncoordinated Asp112 was found to play multiple roles to promote the binding of dioxygen at the trinuclear Cu center and to accelerate the conversion of dioxygen to water molecules by facilitating the supply of H+ to the reaction intermediates.